System and method for actuating a subterranean valve to terminate a reverse cementing operation

ABSTRACT

A system and method for closing a subterranean valve ( 22 ) to terminate a reverse cementing operation is disclosed. The system comprises an interrogator ( 44 ) operably associated with the valve ( 22 ) that detects at least one detectable member ( 52 ) that is associated with an interface ( 50 ) between a first fluid ( 48 ) and a cement composition ( 54 ) that is pumped through an annulus ( 26 ) between a pipe string ( 20 ) and a wellbore ( 18 ). The detectable member ( 50 ) is detectable by the interrogator ( 44 ) when the detectable member ( 50 ) comes within communicative proximity with the interrogator ( 44 ). Once the interrogator ( 44 ) detects the detectable member ( 50 ), the interrogator ( 44 ) sends a signal indicating it is time to close the valve ( 22 ), thereby terminating the cementing process and allowing the cement ( 54 ) to set in the annulus ( 26 ) into a hard, substantially impermeable mass.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates, in general, to controlling the actuation of a subterranean valve and, in particular, to a system and method for actuating a subterranean valve upon confirmation that cement has reached the far end of the annulus between the casing and the wellbore during a reverse cementing operation.

BACKGROUND OF THE INVENTION

[0002] Without limiting the scope of the present invention, its background will be described with reference to cementing a string of casing within a wellbore as an example.

[0003] In primary cementing operations carried out in oil and gas wells, a hydraulic cement composition is disposed between the walls of the wellbore and the exterior of a pipe string, such as a casing string, that is positioned within the wellbore. The cement composition is permitted to set in the annulus thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe in the wellbore and bonds the pipe to the walls of the wellbore whereby the undesirable migration of fluids between zones or formations penetrated by the wellbore is prevented.

[0004] One method of primary cementing involves pumping the cement composition down through the casing and then up through the annulus. In this method, the volume of cement required to fill the annulus must be calculated. Once the calculated volume of cement has been pumped into the casing, a cement plug is placed in the casing. A drilling mud is then pumped behind the cement plug such that the cement is forced into and up the annulus from the far end of the casing string to the surface or other desired depth. When the cement plug reaches a float shoe disposed proximate the far end of the casing, the cement should have filled the entire volume of the annulus. At this point, the cement is allowed to dry in the annulus into the hard, substantially impermeable mass.

[0005] It has been found, however, that due to the high pressure at which the cement must be pumped, at a pressure above the hydrostatic pressure of the cement column in the annulus plus the friction pressure of the system, fluid from the cement composition may leak off into a low pressure zone traversed by the wellbore. When such leak off occurs, the remainder of the cement composition near this low pressure zone flash freezes and sets at that location in the annulus. Once this occurs, additional cement cannot be pumped past this location and all the cement in the system sets. Thereafter, remedial cementing operations, commonly referred to as squeeze cementing, must be used to place cement in the remainder of the annulus. In addition, a large mass of cement that was intended to be placed in the annulus must now be drilled out of the casing.

[0006] Accordingly, prior art attempts have been made to avoid the problems associated with fluid leak off into low pressure zones during cementing operations. One method of avoiding such problems is called reverse cementing wherein the cement composition is pumped directly into the annulus. Using this approach, the pressure required to pump the cement to the far end of the annulus is much lower than that required in conventional cementing operations. Thus, the likelihood of flash freezing the cement in the annulus before the entire annulus is filled with cement is significantly reduced.

[0007] It has been found, however, that with reverse cementing it is necessary to identify when the cement begins to enter the far end of the casing such that the cement pumps may be shut off. Continuing to pump cement into the annulus after cement has reached the far end forces cement into the casing, which in turn may necessitate a drill out operation.

[0008] One method of identifying when the cement has reached the far end of the annulus involves running a neutron density tool down the casing on an electric line. The neutron density tool monitors the density out to a predetermined depth into the formation. When the cement begins to replace the drilling mud in the annulus adjacent to the neutron density tool, the neutron density tool senses the change in density and reports to the surface that it is time to stop pumping additional cement into the annulus. Another method of identifying when the cement has reached the far end of the annulus involves running a resistivity tool and a wireless telemetry system down the casing on a wireline. The resistivity tool monitors the resistivity of the fluid in the casing such that when the cement begins to replace the drilling mud in the casing, a wireless signal is sent to the surface indicating it is time to stop pumping additional cement into the annulus.

[0009] It has been found, however, that use of such retrievable tool systems is prohibitively expensive. In fact, numerous neutron density tools and resistivity tools have been ruined during such operations as a result of the cement entering the far end of the casing and contacting these tools.

[0010] Therefore, a need has arisen for a system and method for cementing the annulus between the wellbore and the casing that does not require pumping the cement at pressures that allow for leak off into low pressure zones. A need has also arisen for such a system and method that identify when to stop pumping additional cement into the wellbore. Further, a need has arisen for such a system and method that do not require the use of expensive equipment including tools that must be retrieved from the well once the cementing operation is complete.

SUMMARY OF THE INVENTION

[0011] The present invention disclosed herein comprise a system and method for cementing the annulus between the wellbore and the casing that does not require pumping the cement at pressures that allow for leak off into low pressure zones. The system and method of the present invention identify when to stop pumping additional cement into the wellbore and do not require the use of expensive equipment including tools that must be retrieved from the well once the cementing operation is complete.

[0012] Broadly stated, the system of the present invention comprises at least one interrogator that is operably associated with an actuatable device disposed within a wellbore and at least one detectable member disposed within a fluid. The detectable member is detectable by the interrogator when the detectable member comes in communicative proximity with the interrogator causing the interrogator to send a signal to actuate the actuatable device.

[0013] The system of the present invention may be specifically used for closing a subterranean valve to terminate a reverse cementing operation. This system comprises at least one interrogator operably associated with the valve, an interface between a first fluid and a cement composition that is pumped through an annulus between a pipe string and a wellbore and at least one detectable member associated with the interface that is detectable by the interrogator when the detectable member comes in communicative proximity with the interrogator causing the interrogator to send a signal the close the valve.

[0014] In one embodiment, the interrogator is an oscillator that produces a magnetic field and the detectable member is a resonant circuit. In another embodiment, the interrogator comprises a radio-frequency transmitter circuit that produces a radio-frequency signal and the detectable member is a radio-frequency modulator that modulates the radio-frequency signal and returns the modulated radio-frequency signal to the interrogator. In yet another embodiment of the present invention, the interrogator is a gamma ray detector and the detectable member is a gamma ray source.

[0015] In one embodiment of the present invention, the interface is an interface fluid between the first fluid and the cement composition and the detectable member is disposed within the interface fluid. In another embodiment, the interface is a mud-cement interface and the detectable member is disposed proximate the mud-cement interface.

[0016] Broadly stated, the method of the present invention involves the steps of operably associating at least one interrogator with the actuatable device, disposing at least one detectable member within a fluid, detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator and sending a signal from the interrogator to actuate the actuatable device.

[0017] The method of the present invention may be specifically used for closing a subterranean valve to terminate a reverse cementing operation. In this case, the method involves the steps of operably associating at least one interrogator with the valve, disposing at least one detectable member within an interface between a first fluid and a cement composition, pumping the cement composition through an annulus between a pipe string and a wellbore, detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator and sending a signal from the interrogator to close the valve.

BRIEF DESCRIPTION OF THE DRAWING

[0018] For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:

[0019]FIG. 1 is a schematic illustration of an onshore oil or gas drilling rig operating a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention;

[0020]FIG. 2 is schematic illustration of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention prior to actuating the valve;

[0021]FIG. 3 is schematic illustration of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention following the actuation of the valve;

[0022]FIG. 4 is a block diagram of one embodiment of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention;

[0023]FIG. 5 is a block diagram of another embodiment of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention;

[0024]FIG. 6 is a block diagram of another embodiment of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention;

[0025]FIG. 7 is a flowchart detailing a method for actuating a subterranean valve to terminate a reverse cementing operation of the present invention;

[0026]FIG. 8 is schematic illustration of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention prior to actuating the valve; and

[0027]FIG. 9 is schematic illustration of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention following the actuation of the valve.

DETAILED DESCRIPTION OF THE INVENTION

[0028] While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

[0029] The present invention provides systems and methods for actuating a subterranean valve. Even though the systems and methods are described as being useful in actuating valves during reverse cementing, it should be understood by one skilled in the art that the systems and methods described herein are equally well-suited for actuating valves during other well operations and actuating downhole equipment other than valves.

[0030] Referring to FIG. 1, an onshore oil or gas drilling rig operating a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention is schematically illustrated and generally designated 10. Rig 12 is centered over a subterranean oil or gas formation 14 located below the earth's surface 16. A wellbore 18 extends through the various earth strata including formation 14. Wellbore 18 is lined with a casing string 20. Casing 20 has a valve 22 that is disposed proximate the far end of casing 20. Valve 22 is used to selectively permit and prevent the flow of fluids therethrough. For example, during a reverse cementing operation, valve 22 remains open as drilling fluids 24 is forced from annulus 26 into the far end of casing 20 when cement 28 is pumped, via cement pump 30, into the near end of annulus 26. When the leading edge of cement 28 reaches the far end of casing 20, valve 22 is closed to prevent cement 28 from traveling within casing 20. Thereafter, cement 28 is allowed to set in annulus 26 to form a hard, substantially impermeable mass which physically supports and positions casing 20 in wellbore 18 and bonds casing 20 to the walls of wellbore 18.

[0031] Rig 12 includes a work deck 32 that supports a derrick 34. Derrick 34 supports a hoisting apparatus 36 for raising and lowering pipe strings such as casing 20. Pump 30 on work deck 32 is of conventional construction and is of the type capable of pumping a variety of fluids into the well. Pump 30 includes a pressure measurement device that provides a pressure reading at the pump discharge.

[0032] Referring now to FIG. 2, therein is depicted an enlarged view of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention that is schematically illustrated and generally designated 40. The far end of wellbore 18 is shown with casing 20 disposed therein. Valve 22 is positioned within casing 20 and is in the open position in FIG. 2. Valve 22 may be of any suitable construction that is known in the art such as ball valves, sleeve valves or the like. Valve 22 may be operated mechanically, electrically, electro-mechanically, hydraulically or by other suitable means.

[0033] Valve 22 has an actuator 42 for operating valve 22 between the open and closed positions. Coupled to actuator 42 is a pair of interrogators 44, 46. Interrogators 44, 46 are used to send a signal to actuator 42 when it is time to operate valve 22. In the illustrated configuration, interrogators 44, 46 are used to send a signal to actuator 42 when it is time to operate valve 22 from the open position to the closed position. It should be noted, however, by those skilled in the art the interrogators 44, 46 could alternatively be used to operate valve 22 from the closed position to the open position or could be used to operate other types of actuatable devices. In addition, even though FIG. 2 depicts two interrogators 44, 46, it should become apparent to those skilled in the art that other numbers of interrogators, either a greater number or a lesser number, may be used to signal actuator 42 to operate without departing from the principles of the present invention.

[0034] Wellbore 18 is filled with various fluids. As illustrated, the fluids include a drilling fluid 48, an interface fluid 50 including a plurality of detectable members 52 and a hydraulic cement composition 28. Drilling fluid 48 may be any typical drilling fluid such as a water-based or oil-based drilling fluid. Importantly, drilling fluid 48 is used to contain subsurface pressure. Accordingly, drilling fluid 48 is weighted with various additives so that the hydrostatic pressure of drilling fluid 48 is sufficient to contain subsurface pressure along the entire depth of wellbore 18, thereby preventing blowouts.

[0035] Interface fluid 50 may be any suitably viscous fluid that is capable of maintaining substantial separation between drilling fluid 48 and cement composition 28. In addition, interface fluid 50 is capable of containing and transporting the plurality of detectable members 52 from the surface to the far end of wellbore 18. For example, interface fluid may be a water-based or oil-based fluid.

[0036] Cement composition 28 may be any typical hydraulic cementitious material including those comprising calcium, aluminum, silicon, oxygen and/or sulfur which set and harden by reaction with water. Such hydraulic materials include Portland cements, pozzolana cements, gypsum cements, high aluminum content cements, silica cements and high alkalinity cements. Portland cements are generally preferred for use in accordance with the present invention. Portland cements of the types defined and described in API Specification for Materials and Testing for Well Cements, API Specification 10, 5th Edition, dated Jul. 1, 1990 of the American Petroleum Institute are particularly suitable. Preferred API Portland cements include classes A, B, C, G and H, with API class H being the most preferred.

[0037] The water used in forming cement composition 28 can be from any source provided it does not contain an excess of compounds that adversely affect other components in cement composition 28. Generally, water is present in a cement slurry composition of this invention in an amount in the range of from about 25% to about 100% by weight of hydraulic material therein and, more preferably, in an amount in the range of from about 30% to about 75% by weight of hydraulic material therein. In addition, various dispersing agents can also be utilized in cement composition 28. The dispersing agent functions to facilitate the dispersal of the solids in the water, and allows the use of smaller amounts of water than is the case without the dispersing agent.

[0038] The plurality of detectable members 52 are suspended in interface layer 50 and circulate with interface layer 50 through annulus 26 and into casing 20 toward valve 22 as cement composition 28 is pumped into annulus 26 at the surface. When one or more of the detectable members 52 come within the communicative proximity of one or both of the interrogators 44, 46, interrogators 44, 46 identify the presence of detectable members 52 and send a signal to actuator 42 to close valve 22.

[0039] As detectable members 52 are associated with interface fluid 50, when detectable members 52 are detected, interface fluid 50 is near valve 22. When interface fluid 50 is near valve 22, annulus 26 is entirely filled with cement 28. Thereafter, valve 22 is closed which sends a pressure signal through the column of cement 28 in annulus 26 indicating that the cement pumps at the surface should be shut off. As best seen in FIG. 3, once detectable members 52 are within the communicative proximity of interrogators 44, 46, actuator 42 closes valve 22 which prevents cement 28 from entering the portion of casing string 20 above valve 22.

[0040] The detailed operation of various embodiments of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention will now be discussed. Referring to FIG. 4, interrogator 60 and detectable member 62, which is disposed within interface fluid 50 between drilling fluid 48 and cement 28, are depicted in communicative proximity to one another. Interrogator 60 is an electronic identification system that utilizes a magnetic field modulation system to monitor for the presence of detectable members 62. Interrogator 60 creates a magnetic field 64 that becomes unbalanced or detuned when one or more detectable member 62 pass through magnetic field 64.

[0041] Several different types of detectable members 62 are suitable for use with interrogator 60. In one type, the functional portion of detectable member 60 consists of either an antenna and diode or an antenna and capacitors forming a resonant circuit. When placed in electromagnetic field 64 generated by interrogator 60, the antenna-diode marker generates harmonics of the interrogating frequency in the receiving antenna. The resonant circuit marker causes an increase in absorption of the transmitted signal so as to reduce the signal in a receiving coil. The detection of the harmonic or signal level change by interrogator 60 indicates the presence of detectable member 62.

[0042] A second type of detectable member 60 includes a first elongated element of high magnetic permeability ferromagnetic material disposed adjacent to at least a second element of ferromagnetic material having higher coercivity than the first element. When subjected to an interrogation frequency of electromagnetic radiation, detectable member 62 causes harmonics of the interrogating frequency to be developed in the receiving coil of interrogator 60. The detection of such harmonics by interrogator 60 indicates the presence of detectable member 62.

[0043] When the detectable member 62 is exposed to a dc magnetic field, the state of magnetization in the second element changes and, depending upon the design of detectable member 62, either the amplitude of the harmonics chosen for detection is significantly reduced, or the amplitude of the even numbered harmonics is significantly changed. Either of these changes can be readily detected by interrogator 60.

[0044] In the illustrated embodiment, interrogator 60 includes an oscillator 66 that applies a sinusoidal current to two substantially identical electromagnetic field producing units 68. Field producing units 68 may be of similarly constructed conducting coils. The lines of the magnetic field produced by the coils are indicated by lines 64.

[0045] Any perturbation in the fields produced by detectable member 62 is detected by a field detector unit 70. Detector unit 70 can be a coil in which the time varying fields induce a voltage. It should be noted that in the absence of a field perturbing object, such as detectable member 62 when it is generally disposed in detectable proximity of the field detector unit 70, the field is balanced.

[0046] The signals produced by detector unit 70 are amplified by an amplifier 72. The output signal of amplifier 72 is filtered by a filter 74. Filter 74 provides a means of eliminating any detected spurious signals at frequencies differing from the electromagnetic field frequency resulting from the interaction of detectable member 62 in field 64 and therefore provides a narrow ban signal of the desired frequency. The output of filter 74 is amplified by an amplifier 76 to provide a sufficient signal level to drive both phase comparator 78 and amplitude comparator 80.

[0047] A portion of the output signal of amplifier 76 is applied to the amplitude comparator circuit 80. When the output signal of amplifier 76 is between predetermined values, a positive logic signal is applied to detection logic circuits 82. Another portion of the output of amplifier 76 is applied to phase comparator circuit 78. The phase of the amplifier output signal is compared with the phase of oscillator 66. When the phases of the two signals differ by a predetermined value, a positive-logic signal is applied to detection logic circuits 82. The simultaneous presence of the amplitude-related and the phase-related logic signals are necessary to activate the detection logic circuits 82. Upon application of the proper positive logic signals to logic circuits 82, an activate signal is applied to actuator 42. Valve actuator 42 triggers an actuation event such as the closing of valve 22.

[0048] Referring next to FIG. 5, another embodiment a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention is depicted. An interrogator 90 and a detectable member 92, which is disposed within interface fluid 50 between drilling fluid 48 and cement 28, are positioned within communicative proximity of one another. Together, interrogator 90 and detectable member 92 may, for example, form a radio-frequency identification (RFID) system. Interrogator 90 comprises a power source 94, an interrogating signal generator 96 with a sending transducer or antenna 98. In addition, interrogator 90 also comprises an amplifier and demodulator 100 operably connected to a signal receiving transducer or an antenna 102. In the illustrated embodiment, the interrogating signal 104 and the response signal 106 are typically radio-frequency (rf) signals produced by an rf transmitter circuit.

[0049] Detectable member 92 comprises a signal receiving and reflecting antenna 108 and a reflector modulator 110 for modulating interrogating signal 104 received by the antenna 108 as well as for reflecting the modulated signal, response signal 106, from antenna 108. As can be seen from FIG. 5, the power source 94 powers interrogating signal generator 96 to send interrogating signal 104 from antenna 98. Preferably, power source 94 is four AA batteries. Interrogating signal 104 from antenna 98 passes through the fluid medium and is received by antenna 108 at detectable member 92. Modulator 110 modulates the signal in accordance with information desired and reflects the amplitude modulated signal, response signal 106, from antenna 108 to antenna 102. Antenna 102 send the signal to amplifier and demodulator 100 which processes the signal to determine whether the response is from a detectable member 92. Upon receipt of the proper response signal, amplifier and demodulator 100 sends an activate signal to valve actuator 42. Valve actuator 42 triggers an actuation event such as the closing of valve 22.

[0050] It should be noted that interrogating signal 104 generated by interrogator 90 need not be a continuous wave or constant in amplitude and/or frequency. It may be appropriate in some applications to generate an interrogating signal 104 that is intermittent. This might be done for various reasons such as conserving power. Many combinations and variations are possible as will be readily recognizable to those skilled in the art.

[0051] Referring now to FIG. 6, another embodiment a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention is depicted. An interrogator 120 and a detectable member 122 are shown in communicative proximity to one another. Interrogator 120 is a gamma ray detecting system that detects gamma rays 124 originating close to interrogator 120 from detectable member 122 that is a radioactive source, which is disposed within interface fluid 50 between drilling fluid 48 and cement 28. Detectable member 122 emits gamma rays 124 that travel only a short distance before being scattered or absorbed.

[0052] A variety of gamma-emitting tracer isotopes are suitable for use within detectable member 122, including but not limited to Gold¹⁹⁸, Xenon¹³³, Iodine¹³¹, Rubidium⁸⁶, Chromium⁵¹, Iron59, Antimony¹²⁴, Stontium⁸⁵, Cobalt⁵⁸, Iridium¹⁹², Scandium⁴⁶, Zinc⁶⁵, Siler¹¹⁰, Cobalt⁵⁷, Cobalt⁶⁰ and Krypton⁸⁵. During the cementing treatment, detectable member 122 regularly emits gamma rays 124, which move through the subterranean system in a random direction for a distance of perhaps one meter, and in the process are scattered and/or absorbed by the subterranean formation and steel tubular elements such as casing 20. Since gamma rays 124 from detectable member 122 travel only a short distance before being absorbed, the gamma rays 124 that impinge upon interrogator 120 will have originated from a location close to interrogator 120. In this manner, interrogator 120 is able to detect when cement 28 has progressed to the far end of wellbore 18 proximate valve 22. Once detection occurs, valve 22 may be closed and the pumping of additional cement 28 is stopped before the interior of casing 20 is cemented.

[0053] Interrogator 120 may be a conventional gamma detector comprises, for example, a thallium activated sodium iodide crystal 126 coupled to a low noise photomultiplier 128 having appropriate electronics associated therewith all of which is encased in lead shielding. Upon detection of the proper gamma ray signal 124, an activation signal is sent from photomultiplier 128 to valve actuator 42 such that valve 22 may be closed.

[0054] Referring now to FIG. 7, a flowchart outlining the method for actuating a subterranean valve to terminate a reverse cementing operation of the present invention is depicted. At block 130, the valve equipped with the interrogator and valve actuator is lowered into the wellbore. The valve can be lowered with the casing string as an attachment to the casing string or, the valve could alternatively be lowered into the well after the casing string has been put into place.

[0055] At block 132, detectable members are placed in the interface fluid and the interface fluid is pumped into the annulus. At block 134, cement is pumped into the annulus. While cement is continuously pumped into the annulus, at decision 136, the interrogator is attempting to detect whether the detectable members are proximate the valve. As long as no detectable members are detected, the pumping of additional cement into the annulus continues. When the interrogator detects the detectable member at block 138, the interrogator sends a signal to the valve actuator at block 140.

[0056] At block 142, the actuator closes the valve such that no additional fluid may flow into the casing. This creates a pressure signal that is detected at the hydraulic pump at block 144. The cement pumping is discontinued at block 146. The cement in the annulus is allowed to set and form a hard, substantially impermeable mass which physically supports and positions the casing in the wellbore and bonds the casing to the walls of the wellbore in block 148.

[0057] Referring now to FIG. 8, therein is depicted an enlarged view of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention that is schematically illustrated and generally designated 150. The far end of wellbore 18 is shown with casing 20 disposed therein. Valve 22 is positioned within casing 20 and is in the open positioned in FIG. 8. Valve 22 has an actuator 42 for operating valve 22 between the open and closed positions. Coupled to actuator 42 is a pair of interrogators 44, 46. Interrogators 44, 46 are used to send a signal to actuator 42 when it is time to operate valve 22. In the illustrated configuration, interrogators 44, 46 are used to send a signal to actuator 42 when it is time to operate valve 22 from the open position to the closed position.

[0058] In the illustrated embodiment, wellbore 18 is filled with two fluids, namely, drilling fluid 48 and hydraulic cement composition 28 which form a mud-cement interface 152 therebetween. A plurality of detectable members 52 are disposed proximate the mud-cement interface 152 such that detectable members 52 circulate through annulus 26 and into casing 20 toward valve 22 as cement composition 28 is pumped into annulus 26 at the surface. When one or more of the detectable members 52 come within the communicative proximity of one or both of the interrogators 44, 46, interrogators 44, 46 identify the presence of detectable members 52 and send a signal to actuator 42 to close valve 22.

[0059] As detectable members 52 are associated with mud-cement interface 152, when detectable members 52 are detected, mud-cement interface 152 is near valve 22. When mud-cement interface 152 is near valve 22, annulus 26 is entirely filled with cement 28. Thereafter, valve 22 is closed which sends a pressure signal through the column of cement 28 in annulus 26 indicating that the cement pumps at the surface should be shut off. As best seen in FIG. 9, once detectable members 52 are within the communicative proximity of interrogators 44, 46, actuator 42 closes valve 22 which prevents cement 28 from entering the portion of casing string 20 above valve 22.

[0060] While this invention has been described with a reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments. 

What is claimed is:
 1. A system for actuating an actuatable device in a subterranean zone penetrated by a wellbore comprising: at least one interrogator operably associated with the actuatable device; and at least one detectable member disposed within a fluid, the detectable member being detectable by the interrogator when the detectable member comes in communicative proximity with the interrogator causing the interrogator to send a signal to actuate the actuatable device.
 2. The system as recited in claim 1 wherein the interrogator comprises an oscillator that produces a magnetic field.
 3. The system as recited in claim 1 wherein the interrogator comprises a radio-frequency transmitter circuit that produces a radio-frequency signal.
 4. The system as recited in claim 1 wherein the interrogator comprises a gamma ray detector that detects gamma rays.
 5. The system as recited in claim 1 wherein the detectable member comprises a resonant circuit.
 6. The system as recited in claim 1 wherein the detectable member comprises a radio-frequency modulator.
 7. The system as recited in claim 1 wherein the detectable member comprises a gamma ray source.
 8. The system as recited in claim 1 wherein the fluid comprises an interface fluid between a drilling fluid and a cement composition and wherein the detectable member is disposed within the interface fluid.
 9. The system as recited in claim 1 wherein the fluid comprises a mud-cement interface and wherein the detectable member is disposed proximate the mud-cement interface.
 10. A system for closing a subterranean valve to terminate a reverse cementing operation comprising: at least one interrogator operably associated with the valve; an interface between a first fluid and a cement composition that is pumped through an annulus between a pipe string and a wellbore; and at least one detectable member associated with the interface, the detectable member being detectable by the interrogator when the detectable member comes in communicative proximity with the interrogator causing the interrogator to send a signal to close the valve.
 11. The system as recited in claim 10 wherein the interrogator comprises an oscillator that produces a magnetic field and wherein the detectable member comprises a resonant circuit.
 12. The system as recited in claim 10 wherein the interrogator comprises a radio-frequency transmitter circuit that produces a radio-frequency signal and wherein the detectable member comprises a radio-frequency modulator.
 13. The system as recited in claim 10 wherein the interrogator comprises a gamma ray detector that detects gamma rays and wherein the detectable member comprises a gamma ray source.
 14. The system as recited in claim 10 wherein the interface further comprises an interface fluid between the first fluid and the cement composition and wherein the detectable member is disposed within the interface fluid.
 15. The system as recited in claim 10 wherein the interface further comprises a mud-cement interface and wherein the detectable member is disposed proximate the mud-cement interface.
 16. A system for closing a subterranean valve to terminate a reverse cementing operation comprising: at least one interrogator that produces a balanced magnetic field, the interrogator operably associated with the valve; an interface between a first fluid and a cement composition that is pumped through an annulus between a pipe string and a wellbore; and at least one detectable member associated with the interface, the detectable member unbalancing the magnetic field when the detectable member comes in communicative proximity with the interrogator causing the interrogator to send a signal to close the valve.
 17. The system as recited in claim 16 wherein the interface further comprises an interface fluid between the first fluid and the cement composition and wherein the detectable member is disposed within the interface fluid.
 18. The system as recited in claim 16 wherein the interface further comprises a mud-cement interface and wherein the detectable member is disposed proximate the mud-cement interface.
 19. A system for closing a subterranean valve to terminate a reverse cementing operation comprising: an interrogator that transmits an interrogating signal and receives a response signal, the interrogator operably associated with the valve; an interface between a first fluid and a cement composition that is pumped through an annulus between a pipe string and a wellbore; and at least one detectable member associated with the interface, the detectable member transmitting the response signal in reply to the interrogating signal when the detectable member comes in communicative proximity with the interrogator causing the interrogator to send a signal to close the valve.
 20. The system as recited in claim 19 wherein the interrogating signal and response signal are radio-frequency signals.
 21. The system as recited in claim 19 wherein the interface further comprises an interface fluid between the first fluid and the cement composition and wherein the detectable member is disposed within the interface fluid.
 22. The system as recited in claim 19 wherein the interface further comprises a mud-cement interface and wherein the detectable member is disposed proximate the mud-cement interface.
 23. A system for closing a subterranean valve to terminate a reverse cementing operation comprising: at least one interrogator that detects gamma rays, the interrogator operably associated with the valve; an interface between a first fluid and a cement composition that is pumped through an annulus between a pipe string and a wellbore; and at least one detectable member associated with the interface, the detectable member having a source that emits gamma rays such that when the detectable member comes in communicative proximity with the interrogator, the interrogator sends a signal to close the valve.
 24. The system as recited in claim 23 wherein the interface further comprises an interface fluid between the first fluid and the cement composition and wherein the detectable member is disposed within the interface fluid.
 25. The system as recited in claim 23 wherein the interface further comprises a mud-cement interface and wherein the detectable member is disposed proximate the mud-cement interface.
 26. A method for actuating an actuatable device in a subterranean zone penetrated by a wellbore comprising the steps of: operably associating at least one interrogator with the actuatable device; disposing at least one detectable member within a fluid; detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator; and sending a signal from the interrogator to actuate the actuatable device.
 27. The method as recited in claim 26 wherein the step of detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator further comprises producing a magnetic field with an oscillator in the interrogator and unbalancing the magnetic field with a resonant circuit in the detectable member.
 28. The method as recited in claim 26 wherein the step of detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator further comprises producing a radio-frequency signal with a radio-frequency transmitter circuit in the interrogator, modulating the radio-frequency signal with the detectable member and returning the modulated radio-frequency signal to the interrogator.
 29. The method as recited in claim 26 wherein the step of detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator further comprises detecting gamma rays with a gamma ray detector in the interrogator and emitting gamma rays from a gamma ray source in the detectable member.
 30. The method as recited in claim 26 wherein the step of disposing at least one detectable member within a fluid further comprises disposing the at least one detectable member within an interface fluid between a drilling fluid and a cement composition.
 31. The method as recited in claim 26 wherein the step of disposing at least one detectable member within a fluid further comprises disposing the at least one detectable member proximate a mud-cement interface.
 32. A method for closing a subterranean valve to terminate a reverse cementing operation comprising the steps of: operably associating at least one interrogator with the valve; disposing at least one detectable member within an interface between a first fluid and a cement composition; pumping the cement composition through an annulus between a pipe string and a wellbore; detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator; and sending a signal from the interrogator to close the valve.
 33. The method as recited in claim 32 wherein the step of detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator further comprises producing a magnetic field with an oscillator in the interrogator and unbalancing the magnetic field with a resonant circuit in the detectable member.
 34. The method as recited in claim 32 wherein the step of detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator further comprises producing a radio-frequency signal with a radio-frequency transmitter circuit in the interrogator, modulating the radio-frequency signal with the detectable member and returning the modulated radio-frequency signal to the interrogator.
 35. The method as recited in claim 32 wherein the step of detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator further comprises detecting gamma rays with a gamma ray detector in the interrogator and emitting gamma rays from a gamma ray source in the detectable member.
 36. The method as recited in claim 32 wherein the step of disposing at least one detectable member within an interface between a first fluid and a cement composition further comprises disposing the at least one detectable member within an interface fluid between the first fluid and the cement composition.
 37. The method as recited in claim 32 wherein the step of disposing at least one detectable member within an interface between a first fluid and a cement composition further comprises disposing the at least one detectable member proximate a mud-cement interface.
 38. A method for closing a subterranean valve to terminate a reverse cementing operation comprising the steps of: operably associating at least one interrogator with the valve; producing a balanced magnetic field with the interrogator; disposing at least one detectable member within an interface between a first fluid and a cement composition; pumping the cement composition through an annulus between a pipe string and a wellbore; unbalancing the magnet field by bringing the detectable member within communicative proximity of the interrogator; detecting the detectable member with the interrogator; and sending a signal from the interrogator to close the valve.
 39. The method as recited in claim 38 wherein the step of disposing at least one detectable member within an interface between a first fluid and a cement composition further comprises disposing the at least one detectable member within an interface fluid between the first fluid and the cement composition.
 40. The method as recited in claim 38 wherein the step of disposing at least one detectable member within an interface between a first fluid and a cement composition further comprises disposing the at least one detectable member proximate a mud-cement interface.
 41. A method for closing a subterranean valve to terminate a reverse cementing operation comprising the steps of: operably associating at least one interrogator with the valve; transmitting a interrogating signal from the interrogator; disposing at least one detectable member within an interface between a first fluid and a cement composition; pumping the cement composition through an annulus between a pipe string and a wellbore; transmitting a reply signal from the detectable member in response to the interrogating signal when the detectable member is within communicative proximity of the interrogator; receiving the reply signal with the interrogator, thereby detecting the detectable member; and sending a signal from the interrogator to close the valve.
 42. The method as recited in claim 41 wherein the step of transmitting an interrogating signal from the interrogator further comprises transmitting a radio-frequency interrogating signal and wherein the step of transmitting a reply signal from the detectable member in response to the interrogating signal further comprises modulating the radio-frequency interrogating signal and transmitting the modulated radio-frequency interrogating signal as the reply signal.
 43. The method as recited in claim 41 wherein the step of disposing at least one detectable member within an interface between a first fluid and a cement composition further comprises disposing the at least one detectable member within an interface fluid between the first fluid and the cement composition.
 44. The method as recited in claim 41 wherein the step of disposing at least one detectable member within an interface between a first fluid and a cement composition further comprises disposing the at least one detectable member proximate a mud-cement interface.
 45. A method for closing a subterranean valve to terminate a reverse cementing operation comprising the steps of: operably associating at least one interrogator with the valve; disposing at least one detectable member within an interface between a first fluid and a cement composition; pumping the cement composition through an annulus between a pipe string and a wellbore; emitting gamma rays from a source in the detectable member; detecting the gamma rays from the detectable member with a gamma ray detector in the interrogator when the detectable member comes within communicative proximity of the interrogator; and sending a signal from the interrogator to close the valve.
 46. The method as recited in claim 45 wherein the step of disposing at least one detectable member within an interface between a first fluid and a cement composition further comprises disposing the at least one detectable member within an interface fluid between the first fluid and the cement composition.
 47. The method as recited in claim 45 wherein the step of disposing at least one detectable member within an interface between a first fluid and a cement composition further comprises disposing the at least one detectable member proximate a mud-cement interface. 